Table 3. Characteristics of subjects, parental and household environmental factors in the two study periods.
| Characteristics | Period 1 | Period 2 | P for period difference |
|---|---|---|---|
| Total | 2,517 | 3,152 | |
| Age (year, mean ± SD) | 9.81±1.60 | 8.88±1.38 | <0.001 |
| District, n (%) | <0.001 | ||
| Urban | 1,923 (76.4) | 1,985 (63.0) | |
| Suburban | 594 (23.6) | 1,167 (37.0) | |
| Gender, n (%) | <0.001 | ||
| Male | 1,253 (49.8) | 1,798 (57.0) | |
| Female | 1,264 (50.2) | 1,354 (43.0) | |
| Environmental tobacco smoke (ETS), n (%) | 2,083 (86.6) | 1,382 (45.9) | <0.001 |
| Coal use, n (%) | 1,198 (47.6) | 155 (4.9) | <0.001 |
| Kitchen smoke, n (%) | 1,479 (58.8) | 231 (7.3) | <0.001 |
| Sleep in own room, n (%) | 713 (28.3) | 1,573 (51.2) | <0.001 |
| Sleep in own bed, n (%) | 1,599 (63.6) | 1,938 (63.4) | 0.916 |
| Breast feeding, n (%) | 1,707 (67.8) | 2,402 (82.7) | <0.001 |
| Father occupation1, n (%) | <0.001 | ||
| Blue collar2 | 1,490 (59.8) | 1,439 (48.1) | |
| White collar3 | 964 (38.7) | 1,143 (38.2) | |
| Mother occupation1, n (%) | <0.001 | ||
| Blue collar2 | 1,470 (59.1) | 1,195 (42.1) | |
| White collar3 | 894 (36.0) | 1,291 (45.4) | |
| Father education, n (%) | <0.001 | ||
| Less than high school | 2,124 (85.2) | 2,283 (76.1) | |
| University and above | 368 (14.8) | 718 (23.9) | |
| Mother education, n (%) | <0.001 | ||
| Less than high school | 2,331 (93.7) | 2,364 (79.0) | |
| University and above | 156 (6.3) | 628 (21.0) | |
| Father diseases, n (%) | |||
| Asthma | 38 (1.5) | 23 (0.8) | 0.010 |
| Bronchitis | 373 (14.9) | 179 (6.1) | <0.001 |
| Mother diseases, n (%) | |||
| Asthma | 34 (1.4) | 15 (0.5) | 0.001 |
| Bronchitis | 220 (8.8) | 137 (4.7) | <0.001 |
1, occupations not belonging to the below types or parents had multiple occupations are not shown in the chart. 2, farmer and worker who works in a factory or in the production of chemicals, fertilizers, and paints. 3, businessman, education or medical staff, civil servant, and military personnel.